aco: Convert to use u8 literal for Unicode character to fixes msvc warning

Warning:
aco_register_allocation.cpp(383): warning C4819: The file contains a character that cannot be represented in the current code page (0). Save the file in Unicode format to prevent data loss

This warning was treated as error with compiling with msvc
u8 is belongs to c11 standard so it's safe to use it

Signed-off-by: Yonggang Luo <luoyonggang@gmail.com>
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/18682>

src/amd/compiler/aco_register_allocation.cpp

@@ -379,16 +379,16 @@ UNUSED void
 print_reg(const RegisterFile& reg_file, PhysReg reg, bool has_adjacent_variable)
 {
    if (reg_file[reg] == 0xFFFFFFFF) {
-      printf("☐");
+      printf(u8"☐");
    } else if (reg_file[reg]) {
       const bool show_subdword_alloc = (reg_file[reg] == 0xF0000000);
       if (show_subdword_alloc) {
          const char* block_chars[] = {
             // clang-format off
-            "?", "▘", "▝", "▀",
-            "▖", "▌", "▞", "▛",
-            "▗", "▚", "▐", "▜",
-            "▄", "▙", "▟", "▉"
+            u8"?", u8"▘", u8"▝", u8"▀",
+            u8"▖", u8"▌", u8"▞", u8"▛",
+            u8"▗", u8"▚", u8"▐", u8"▜",
+            u8"▄", u8"▙", u8"▟", u8"▉"
             // clang-format on
          };
          unsigned index = 0;
@@ -401,14 +401,14 @@ print_reg(const RegisterFile& reg_file, PhysReg reg, bool has_adjacent_variable)
       } else {
          /* Indicate filled register slot */
          if (!has_adjacent_variable) {
-            printf("█");
+            printf(u8"█");
          } else {
             /* Use a slightly shorter box to leave a small gap between adjacent variables */
-            printf("▉");
+            printf(u8"▉");
          }
       }
    } else {
-      printf("·");
+      printf(u8"·");
    }
 }